Such drug delivery devices make it possible to control the release of drugs in the gastrointestinal tract. The drug delivery may take place in accordance with a predetermined delivery schedule and/or may be triggered by external signals or environmental conditions. The device may include additional electronics, sensors and communication devices for controlling the drug delivery. In many swallowable drug delivery devices, the drug release is effected using a displacement based actuator system. For example, a piston may push a predetermined amount of the drug through the dispensing hole.
The dispensing hole often is an open orifice. However, an open orifice introduces the possibility for exchange of material between the reservoir and outside environment, resulting, for example, in delivery of the drug before the intended time and a reduction of the amount delivered when intended. The main processes involved are diffusion and convection. Diffusion, because of the open connection between the inside and the outside of the capsule. Convection, because of small differences in specific weight of the substance stored in the capsule and the fluid outside. E.g. when the fluid in the capsule is heavier than the fluid in the intestines and the hole is directed downwards the fluid in the capsule flows out and will be replaced by the fluid of the intestines. Both processes may be slowed down by reduction in the exit hole cross-sectional size, extending the length of the exit hole and increasing the viscosity of the material in the reservoir. However the hole dimensions and the viscosity of the medicine to be administered must be chosen such that it allows the actuator to dispense the medicine.
Often, a valve is used for separating the drug reservoir from the outside environment. Valves which operate in small spaces, provide good sealing and use low power are however very difficult to implement. It would thus be advantageous to avoid diffusion or convection of the drug without the use of a valve.